The widespread use of full-color copiers that employ electrophotographic systems in recent years has been accompanied by increased demands for energy-saving measures. As a specific energy-saving measure, investigations have been carried out into technology that brings about fixing at lower fixation temperatures in order to lower the power consumption in the fixing step.
One strategy for achieving this is to lower the glass transition temperature (Tg) of the toner. However, when just a lowering of the Tg is implemented by itself, the heat-resistant storability of the toner is lowered and clumping is then prone to appear in high temperature environments due to the occurrence of aggregation between toner particles in contact with each other. The heat-resistant storability of the toner must therefore be improved in order to pursue improvements in the low-temperature fixability.
In response to this problem, various efforts at producing a toner having a capsule structure have been proposed. For example, improving the heat-resistant storability has been pursued by coating the surface of a core particle comprising a low Tg resin with the fine powder of a resin having a higher Tg than that of the core particle and then forming a surface coat layer of the fine resin powder by performing a surface treatment with a hot air current (refer to Patent Document 1).
However, while the toner described in Patent Document 1 does have an improved heat-resistant storability, the surface of the toner particle is nevertheless coated with the fine powder of a high Tg resin, and as a consequence the low-temperature fixability possessed by the core particle of the toner cannot be thoroughly manifested, for example, in high-speed equipment (high-speed equipment operating at 80 prints/minute or more), and a large energy consumption may then be required for fixing.